Dielectric ceramic composition

ABSTRACT

A dielectric ceramic composition comprising a first compound having the general formula, aCaTiO 3 —(1−a)Ca(Al ½ Nb ½ )O 3  in which 0.4≦a≦0.6.  
     Preferably, it further contains a second compound selected from the group consisting of zirconium oxide (ZrO 2 ), manganese oxide (MnO 2 ) and antimony trioxide (Sb 2 O 3 ), with the second compound present in an amount no more than 2 parts by weight relative to 100 parts by weight of the first compound.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a dielectric ceramic compositioncomprising calcium, titanium, aluminium, niobium and oxygen, which isfavorable for dielectric resonators for use in a microwave region of afew GHz zone.

[0003] The dielectric ceramic composition of the invention is used notonly for dielectric resonators but also for substrates for microwaveICs, dielectric control rods, etc.

[0004] 2. Description of the Related Art

[0005] With the recent tendency in the art toward highly integratedmicrowave circuits, desired are small-sized high-performance dielectricresonators for them. The requirements of dielectric ceramic compositionsfor such dielectric resonators are that their relative dielectricconstant ε_(r) is large, that the absolute value of the temperaturecoefficient τ_(f) of resonance frequency is small and stable, and thattheir unloaded Q is large.

[0006] Some dielectric ceramic compositions essentially comprising TiO₂,BaO—TiO₂ or the like are known, but they are difficult to industrializeas their temperature coefficient is large and their dielectric loss in amicrowave zone is large.

[0007] Other dielectric ceramic compositions having a perovskitestructure of, for example, Ba(Mg_(⅓)Ta_(⅔))O₃, Ba(Zn_(⅓)Ta_(⅔))O₃,Ba(Zn_(⅓)Nb_(⅔))O₃ or the like are known, but their dielectric constantis small. Therefore, for example, when they are formed into resonatorsusable in a microwave zone of from 0.1 to 5 GHz, the size of theresonators is inevitably large.

[0008] One object of the present invention is to provide a dielectricceramic composition favorable for dielectric resonators, especially forthose for use in a microwave zone of from 0.1 to 5 GHz.

[0009] Another object of the invention is to provide a dielectricceramic composition having a high dielectric constant ε_(r), a high Qvalue, and a small and stable absolute value of the temperaturecoefficient τ_(f) of resonance frequency.

SUMMARY OF THE INVENTION

[0010] We, the present inventors have found that, of many constituentelements used in dielectric ceramic compositions, a specific ceramiccomposition comprising a combination of calcium, titanium, aluminium,niobium and oxygen attains the above-mentioned objects, and havecompleted the present invention.

[0011] Specifically, the invention provides a dielectric ceramiccomposition comprising a first compound of a general formula,aCaTiO₃—(1−a)Ca(Al_(½)Nb_(½))O₃ with 0.4≦a≦0.6.

[0012] The invention also provides a dielectric ceramic compositioncomprising the first compound as above and containing, as a secondcompound, at least one of zirconium oxide (ZrO₂), manganese oxide (MnO₂)and antimony trioxide (Sb₂O₃), in which the amount of the secondcompound is at most 2 parts by weight relative to 100 parts by weight ofthe first compound.

BRIEF DESCRIPTION OF THE DRAWING

[0013]FIG. 1 is an X-ray diffraction pattern of one example of thedielectric ceramic composition of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The dielectric ceramic composition of the invention comprises afirst compound of a general formula, aCaTiO₃—(1−a)Ca(Al_(½)Nb_(½))O₃with 0.4≦a≦0.6. The composition has a large relative dielectricconstant, and therefore can be formed into small-sized resonators havingthe advantages of large unloaded Q and small temperature coefficientτ_(f) of resonance frequency.

[0015] Preferably, the dielectric ceramic composition of the inventioncontains, as a second compound, at most 2 parts by weight, relative to100 parts by weight of the first compound therein, of at least one ofzirconium oxide (ZrO₂), manganese oxide (MnO₂) and antimony trioxide(Sb₂O₃). More preferably, the second compound content of the compositionfalls between 0.2 and 2 parts by weight. Containing the second compound,the unloaded Q of the composition is greatly increased.

[0016] The first compound of the dielectric ceramic composition of theinvention is a composite oxide containing metal elements of Ca, Ti, Aland Nb. The constitution of the first compound is specifically definedas above, and the reason for it is as follows:

[0017] In the formula that represents the first compound, 0.4≦a≦0.6. Ifa is too large, τ_(f) of the dielectric ceramic composition increases onthe positive side, and is over 50 ppm/° C. On the other hand, if a istoo small, the dielectric constant of the composition lowers, and τ_(f)thereof increases on the negative side to overstep −50 ppm/° C.

[0018] The second compound of the dielectric ceramic composition of theinvention is at least one of zirconium oxide, manganese oxide andantimony trioxide. The additives to be the second compound may bezirconium oxide (ZrO₂), manganese oxide (MnO₂) and antimony trioxide(Sb₂O₃) themselves, but may also be zinc, manganese and antimonycarbonates and hydroxides capable of being converted into their oxidesduring the firing process. Regarding the amount of the second compoundthat may be in the composition, the additives may be added to thecomposition so that they satisfy the range of the second compounddefined herein in terms of zirconium oxide (ZrO₂), manganese oxide(MnO₂) and antimony trioxide (Sb₂O₃). The reason why the second compoundcontent of the composition is defined as above is because, if the secondcompound content is too much larger than 2 parts by weight, the unloadedQ of the composition may lowers.

[0019] One preferred example of the method for producing the dielectricceramic composition of the invention is described below.

[0020] Starting materials of calcium carbonate, titanium oxide,aluminium oxide and niobium oxide are mixed in wet in a predeterminedratio, along with a solvent such as water or alcohol. Next, the solventsuch as water or alcohol is removed from the mixture, then the drymixture is ground and calcined in an oxygen-containing gas atmosphere(for example, in air) at 1000 to 1300° C. for about 2 to 10 hours. Theresulting calcined powder is further ground, then mixed and homogenizedalong with an organic binder such as polyvinyl alcohol, dried, stillground, and thereafter shaped under pressure (100 to 1000 kg/cm²). Thethus-shaped cake is fired in an oxygen-containing gas atmosphere such asair at 1350 to 1650° C. to give a dielectric ceramic composition havingthe above-mentioned compositional formula.

[0021] A dielectric ceramic composition containing an additive of any ofzirconium oxide, manganese oxide and antimony trioxide may be producedas follows: The additive is added to the calcined powder prepared in themanner as above, and then mixed in wet along with a solvent such aswater or alcohol. Next, the solvent such as water or alcohol is removedfrom the mixture, and the dry mixture is further mixed and homogenizedalong with an organic binder such as polyvinyl alcohol, dried, stillground, and thereafter shaped under pressure (100 to 1000 kg/cm²). Thethus-shaped cake is fired in an oxygen-containing gas atmosphere such asair at 1350 to 1650° C. to give a dielectric ceramic composition havingthe above-mentioned compositional formula and containing the additive.

[0022] The dielectric ceramic composition thus obtained in the manner asabove is, directly or optionally after processed into a shaped bodyhaving a desired size, used as a material for dielectric resonators,dielectric substrates for microwave ICs, dielectric control rods, etc.In particular, the composition exhibits an excellent effect when formedinto dielectric resonators for use in a zone of from 0.1 to 5 GHz.

[0023] For the starting materials for calcium, titanium, aluminium andniobium, usable are CaCO₃, TiO₂, Al₂O₃, Nb₂O₆, and also carbonates andhydroxides that may be converted into oxides during firing process. Inthe composition of aCaTiO₃—(1−a)Ca(Al_(½)Nb_(½))O₃ in which 0.4≦a≦0.6,even when the amount of some constituent elements increases or decreasesin some degree, or even when some constituent elements are partlysubstituted with any other elements, or even when some additives areadded to the composition, the resulting compositions still have the sameperovskite structure and exhibit the same effect.

EXAMPLES

[0024] The invention is described more concretely with reference to thefollowing Examples, which, however, are not intended to restrict thescope of the invention.

Example 1

[0025] [Sample No. 1]

[0026] Calcium carbonate (CaCO₃) powder, titanium oxide (TiO₂) powder,aluminium oxide (Al₂O₃) powder and niobium oxide (Nb₂O₅) powder were putinto a ball mill along with ethanol, and mixed in wet for 12 hours. Thesolvent, ethanol was removed from the resulting mixture, which was thenground for 1 hour in a grinder and calcined at 1200° C. for 5 hours toobtain a calcined powder of 0.6CaTiO₃—0.4Ca(Al_(½)Nb_(½))O₃.

[0027] Next, a suitable amount of polyvinyl alcohol solution was addedto the calcined powder and uniformly mixed, and the resulting mixturewas pelletized into pellets having a diameter of 10 mmφ and a thicknessof 4 mmt. Then, the pellets were fired and sintered in an air atmosphereat 1500° C. for 2 hours to be a dielectric ceramic composition of theinvention.

[0028] The thus-obtained ceramic composition was cut into pieces havinga suitable size. The pieces were tested according to a dielectricresonance method, and the unloaded Q and the relative dielectricconstant ε_(r) at a resonance frequency f₀ (4 to 6 GHz) of thecomposition were obtained.

[0029] Regarding the temperature dependency of the resonance frequencyof the composition, the pieces were measured at different temperaturesfalling between −40 and 80° C., and the temperature coefficient τ_(f) ofthe composition was obtained. The data obtained are given in Table 1.

[0030] The dielectric ceramic composition obtained herein was analyzedthrough X-ray diffractometry, and was found having a compositeperovskite structure of 0.6CaTiO₃—0.4Ca(Al_(½)Nb_(½))O₃. FIG. 1 showsthe X-ray diffraction pattern of the composition. TABLE 1 CaTiO₃Ca(Al_(1/2)Nb_(1/2))O₃ τ_(f) No. A 1-a ε_(r) f₀Q (ppm/° C.)  1 0.60 0.4057.3 33000 42.5  2 0.58 0.42 55.1 35000 31.2  3 0.55 0.45 53.5 3700020.5  4 0.53 0.47 51.6 39500 11.2  5 0.52 0.48 50.5 41000 4.2  6 0.500.50 48.4 41200 −4.9  7 0.49 0.51 47.0 41000 −8.5  8 0.48 0.52 46.140900 −11.0  9 0.46 0.54 44.9 40700 −15.1  10 0.45 0.55 44.2 41000 −17.6 11 0.44 0.56 43.8 40800 −20.2  12 0.42 0.58 41.5 40500 −29.5  13 0.400.60 40.6 39000 −37.6 *14 0.70 0.30 71.7 28000 129.8 *15 0.30 0.70 36.240000 −56.1

[0031] [Samples No. 2 to No. 15]

[0032] Dielectric ceramic compositions were produced in the same manneras that for sample No. 1, except that the blend ratio of calciumcarbonate, titanium oxide, aluminium oxide and niobium oxide was varied,and these were tested also in the same manner for their characteristics.

[0033] The data obtained are in Table 1, in which the samples markedwith * are comparative samples not falling within the scope of theinvention.

[0034] As is obvious from Table 1, the dielectric ceramic composition ofthe invention has excellent characteristic properties such as a relativedielectric constant of larger than 40, an f₀Q value of not smaller than33000, and τ_(f) falling within a range of ±50 ppm/° C. However, thedielectric ceramic composition not falling within the scope of theinvention have a low dielectric constant or a low f₀Q value, and theabsolute value of their τ_(f) is over 50.

[0035] [Sample No. 16]

[0036] Calcium carbonate (CaCO₃) powder, titanium oxide (TiO₂) powder,aluminium oxide (Al₂O₃) powder and niobium oxide (Nb₂O₅) powder were putinto a ball mill along with ethanol, and mixed in wet for 12 hours. Thesolvent, ethanol was removed from the resulting mixture, which was thenground for 1 hour in a grinder, and calcined at 1200° C. for 5 hours toobtain a calcined powder of 0.6CaTiO₃—0.4Ca(Al_(½)Nb_(½))O₃. Theresulting calcined powder was put into a ball mill along zirconium oxide(ZrO₂) powder and ethanol, and mixed in wet for 12 hours. The solvent,ethanol was removed from the resulting mixture, which was then groundfor 1 hour in a grinder.

[0037] Next, a suitable amount of polyvinyl alcohol solution was addedto the calcined powder and uniformly mixed, and the resulting mixturewas pelletized into pellets having a diameter of 10 mmφ and a thicknessof 4 mmt. Then, the pellets were fired and sintered in an air atmosphereat 1500° C. for 2 hours to be a dielectric ceramic composition of theinvention.

[0038] The thus-obtained ceramic composition was cut into pieces havinga suitable size. The pieces were tested according to a dielectricresonance method, and the unloaded Q and the relative dielectricconstant ε_(r) at a resonance frequency f₀ (4 to 6 GHz) of thecomposition were obtained.

[0039] Regarding the temperature dependency of the resonance frequencyof the composition, the pieces were measured at different temperaturesfalling between −40 and 80° C., and the temperature coefficient τ_(f) ofthe composition was obtained. The data obtained are given in Table 2.

[0040] [Samples No. 17 to No. 26]

[0041] Dielectric ceramic compositions were produced in the same manneras that for sample No. 16, except that the blend ratio of calciumcarbonate, titanium oxide, aluminium oxide, niobium oxide and zirconiumoxide was varied, and these were tested also in the same manner fortheir characteristics.

[0042] The data obtained are in Table 2.

[0043] As is obvious from Table 1 and Table 2, the dielectric ceramiccomposition of the invention has excellent characteristic propertiessuch as a relative dielectric constant of larger than 40, an f₀Q valueof not smaller than 33000, and τ_(f) falling within a range of ±50 ppm/°C. The f₀Q value of the dielectric ceramic composition containing theadditive ZrO₂ increased. However, adding too much the additive to thedielectric ceramic composition did not improve the characteristics ofthe dielectric ceramic composition. TABLE 2 ZrO₂ CaTiO₃Ca(Al_(1/2)Nb_(1/2))O₃ (wt. τ_(f) No. a 1-a pts.) ε_(r) f₀Q (ppm/° C.)16 0.60 0.40 0.2 57.5 34000 43.0 17 0.60 0.40 0.7 58.3 37000 46.5 180.60 0.40 2 59.4 36000 49.3 19 0.55 0.45 0.7 54.2 41500 24.3 20 0.500.50 0.2 48.6 42500 −3.0 21 0.50 0.50 0.7 49.2 45000 0.5 22 0.50 0.50 250.4 44000 5.0 23 0.45 0.55 0.7 45.3 44500 −11.2 24 0.40 0.60 0.2 41.040500 −35.0 25 0.40 0.60 0.7 41.7 43000 −29.5 26 0.40 0.60 2 42.5 42100−25.2

[0044] [Samples No. 27 to No. 31]

[0045] Dielectric ceramic compositions were produced in the same manneras that for sample No. 16, except that they contained a second compound,manganese oxide (MnO₂), and that the blend ratio of calcium carbonate,titanium oxide, aluminium oxide, niobium oxide and manganese oxide wasvaried. These were tested also in the same manner for theircharacteristics.

[0046] In producing these, manganese carbonate (MnCO₃) and not manganeseoxide (MnO₂) was added to the calcined mixture. The additive content ofthe compositions is in terms of manganese oxide (MnO₂).

[0047] The data obtained are given in Table 3.

[0048] As is obvious from Table 1 and Table 3, the dielectric ceramiccomposition of the invention has excellent characteristic propertiessuch as a relative dielectric constant of larger than 40, an f₀Q valueof not smaller than 33000, and τ_(f) falling within a range of ±50 ppm/°C. The f₀Q value of the dielectric ceramic composition containing theadditive MnO₂ increased. However, adding too much the additive to thedielectric ceramic composition did not improve the characteristics ofthe dielectric ceramic composition. TABLE 3 MnO₂ CaTiO₃Ca(Al_(1/2)Nb_(1/2))O₃ (wt. τ_(f) No. a 1-a pts.) ε_(r) f₀Q (ppm/° C.)27 0.60 0.40 0.7 58.1 36000 45.5 28 0.50 0.50 0.2 48.4 42000 −2.5 290.50 0.50 0.7 49.1 44000 0.3 30 0.50 0.50 2 50.3 42500 4.5 31 0.40 0.600.7 41.5 42500 −28.5

[0049] [Samples No. 32 to No. 36]

[0050] Dielectric ceramic compositions were produced in the same manneras that for sample No. 16, except that they contained a second compound,antimony oxide, and that the blend ratio of calcium carbonate, titaniumoxide, aluminium oxide, niobium oxide and antimony oxide was varied.These were tested also in the same manner for their characteristics.

[0051] The data obtained are given in Table 4.

[0052] As is obvious from Table 1 and Table 4, the dielectric ceramiccomposition of the invention has excellent characteristic propertiessuch as a relative dielectric constant of larger than 40, an f₀Q valueof not smaller than 33000, and τ_(f) falling within a range of ±50 ppm/°C. The f₀Q value of the dielectric ceramic composition containing theadditive antimony oxide increased. However, adding too much the additiveto the dielectric ceramic composition did not improve thecharacteristics of the dielectric ceramic composition. TABLE 4 Sb₂O₃CaTiO₃ Ca(Al_(1/2)Nb_(1/2))O₃ (wt. τ_(f) No. a 1-a pts.) ε_(r) f₀Q(ppm/° C.) 32 0.60 0.40 0.7 58.8 37500 48.5 33 0.50 0.50 0.2 49.1 43000−1.5 34 0.50 0.50 0.7 49.8 45100 1.6 35 0.50 0.50 2 50.9 42500 6.0 360.40 0.60 0.7 42.1 43500 −28.2

[0053] [Samples No. 37 to No. 45]

[0054] Dielectric ceramic compositions were produced in the same manneras that for sample No. 16, except that they contained second compounds,any of zirconium oxide, manganese oxide and antimony oxide, and that theblend ratio of calcium carbonate, titanium oxide, aluminium oxide,niobium oxide zirconium oxide, manganese oxide and antimony oxide wasvaried. These were tested also in the same manner for theircharacteristics.

[0055] The data obtained are given in Table 5.

[0056] As is obvious from Table 1 and Table 5, the dielectric ceramiccomposition of the invention has excellent characteristic propertiessuch as a relative dielectric constant of larger than 40, an f₀Q valueof not smaller than 33000, and τ_(f) falling within a range of ±50 ppm/°C. The f₀Q value of the dielectric ceramic composition containing any ofthe additives, zirconium oxide, manganese oxide and antimony oxideincreased. However, adding too much the additives to the dielectricceramic composition did not improve the characteristics of thedielectric ceramic composition. TABLE 5 CaTiO₃ Ca(Al_(½)Nb_(½))O₃ ZrO₂MnO₂ Sb₂O₃ τ_(f) No. a 1-a (wt. pts.) (wt. pts.) (wt. pts.) ε_(r) f₀Q(ppm/° C.) 37 0.60 0.40 0.7 0.7 0 58.1 39500 45.5 38 0.60 0.40 0.7 0 0.758.3 40000 46.5 39 0.50 0.50 0.1 0.1 0 48.4 45000 −3.5 40 0.50 0.50 0.70.7 0 49.0 47500 −0.5 41 0.50 0.50 1 1 0 50.2 47000 4.0 42 0.50 0.50 0.10 0.1 48.6 45500 −3.2 43 0.50 0.50 1 0 1 50.3 46000 4.5 44 0.40 0.60 0.70.7 0 41.5 45500 −28.5 45 0.40 0.60 0.7 0 0.7 41.7 46000 −29.3

[0057] As is obvious from Tables 1 to 5, the dielectric ceramiccomposition of the invention has excellent characteristic propertiessuch as a relative dielectric constant of larger than 40, an f₀Q valueof not smaller than 33000, and τ_(f) falling within a range of ±50 ppm/°C. However, adding too much the additive(s) to the dielectric ceramiccomposition did not improve the characteristics of the dielectricceramic composition.

[0058] The dielectric ceramic compositions of the invention have a highdielectric constant, increased unloaded Q and small temperaturecoefficient τ_(f) of resonance frequency.

[0059] While the invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

What is claimed is:
 1. A dielectric ceramic composition comprising afirst compound having the general formula,aCaTiO₂—(1−a)Ca(Al_(½)Nb_(½))O₃ in which 0.4≦a≦0.6.
 2. The dielectricceramic composition as claimed in claim 1 , further comprising at leasta second compound selected from the group consisting of zirconium oxide(ZrO₂), manganese oxide (MnO₂), and antimony trioxide (Sb₂O₃), with thesecond compound present in an amount no more than 2 parts by weightrelative to 100 parts by weight of the first compound.
 3. The dielectricceramic composition as claimed in claim 2 , wherein the second compoundis zirconium oxide (ZrO₂).
 4. The dielectric ceramic composition asclaimed in claim 2 , wherein the second compound is manganese oxide(MnO₂).
 5. The dielectric ceramic composition as claimed in claim 2 ,wherein the second compound is antimony trioxide (Sb₂O₃).
 6. Thedielectric ceramic composition as claimed in claim 3 , which containsfrom 0.2 to 2 parts by weight of the second compound relative to 100parts by weight of the first compound.
 7. The dielectric ceramiccomposition as claimed in claim 4 , which contains from 0.2 to 2 partsby weight of the second compound relative to 100 parts by weight of thefirst compound.
 8. The dielectric ceramic composition as claimed inclaim 5 , which contains from 0.2 to 2 parts by weight of the secondcompound relative to 100 parts by weight of the first compound.
 9. Adielectric resonator for resonating in a region of resonant frequencybetween about 0.1 and 5 GHz comprising a dielectric ceramic compositionof high dielectric constant and Q value having a first compound of thegeneral formula aCaTiO₃—(1−a)Ca(Al_(½)Nb_(½))O₃ in which 0.4≦a≦0.6wherein the first compound provides a temperature coefficient ofresonance frequency of between −50 ppm/oc to +50 ppm/oc for thedielectric ceramic composition.
 10. A dielectric resonator as claimed inclaim 9 further comprising a second compound selected from the groupconsisting of zirconium oxide (ZrO₂), manganese oxide (MnO₂), andantimony trioxide (Sb₂O₃) wherein the second compound is present in anamount no more than 2 parts by weight relative to 100 parts by weight ofthe first compound.